Interactive rating component main with flexbox and js vanilla

I'm having difficulty with some things. First, I would like to save the input value on click, but I couldn't, so I did it with the num attribute in the function.

Also, I would like to display an alert for when the submit button is clicked without choosing a number. Initially the variable btn has the value undefined. I tried as follows: function onSubmit() { if (btn == undefined){ alert('') } else { state1.style.display = 'none' state2.style.display = 'flex' } }

But the function never enters the else, the value of btn changes to the value of num when the onRating function is called, but soon after it returns to the value undefined. I can't solve this, could someone help me? :(